The present invention relates in general to intraluminal medical devices, and more particularly to guidewires or core wires for intraluminal devices including catheters, and means for proper location of such intraluminal devices within the body.
The use of intraluminal catheters for treatment of various medical problems within the body is well known. It is also well known that a variety of difficulties may be encountered as the catheter is steered through the selected lumen to a desired point within the body. The path may be tortuous and the point of interest may be difficult to locate precisely. To overcome these difficulties, a flexible guidewire may first be inserted into the vascular lumen to the desired location. Once a guidewire is in position, a desired catheter may then be slid over the guidewire to reach the desired situs in the body.
It can readily be seen that it is important to have a guidewire that is flexible enough to traverse the tortuous vascular system. It can also be readily seen that it is important to have a guidewire that is radioscopic such that the physician can verify the position or location of the guidewire within the vascular lumen.
A continuing series of technical improvements and additions have been made in the catheter field to provide devices and methods which can overcome certain of these difficulties. One such series of improvements has resulted in the now well known use of a thin flexible guidewire having a tapered distal section that can be more easily steered through the lumen by forces applied to a proximal section. Because the distal section of a tapered guidewire may lose pushability, another improvement that has been developed is the use of a coiled wire helix which is wrapped around the distal tapered section of the guidewire. The coiled wire helix may improve the pushability of the distal tapered section of the guidewire while maintaining overall flexibility.
An example of a guidewire having a coiled wire helix is disclosed in U.S. Pat. No. 4,619,274 issued to Morrison. Morrison discloses a core member having a proximal and a distal end wherein the core member has a decreasing cross sectional area in a direction toward the distal end. The decreasing cross sectional area is incremental in that the core member comprises a plurality of fixed diameter cylinders which are coupled together by tapered sections. The diameters of the fixed diameter cylinders become smaller in the direction of the distal end of the core member.
Morrison further discloses a tapered coil which is carried and secured to the core element and extends over the core element. The tapered coil has a proximal end and a distal end wherein the diameter of the tapered coil decreases toward the distal end. Furthermore, the coil is formed of wire having a diameter which decreases toward the distal end. The improvements suggested by Morrison may provide some increased pushability while maintaining a degree of flexibility. However, the decreasing diameter core member and tapered coil may limit the pushability of the distal tip of the core member.
Another example of a guidewire having a coiled wire helix is disclosed in U.S. Pat. No. 4,846,186 issued to Box et al. In Box et al., a core member having an initial uniform diameter segment tapers along a uniform portion to a second constant diameter segment. A flexible spring tip surrounds, and is attached to, the second constant diameter segment and extends distally therefrom. The core member again tapers in a region where the flexible spring separates from the core member. Within the flexible spring, a portion of the core member is flattened to increase the flexibility of the distal portion of the core member. The flattened core and spring are brazed together at an extreme distal tip portion to form a distal guidewire tip.
A further variant of a guidewire having a reduced diameter distal portion surrounded by a coil wire helix is disclosed in U.S. Pat. No. 4,538,622 to Samson et al. The guidewire disclosed in Samson et al. includes an elongated stainless steel core wire having a reduced diameter distal portion including two constant diameter portions and two tapered portions.
The reduced diameter distal portion is surrounded by a first proximately disposed coil and a second distally disposed coil. The proximate coil is preferably stainless steel and is soldered at its proximal end to the core wire. The distal coil is preferably formed from a radiopaque material such as gold or platinum to allow location of the distal end of the guidewire by fluoroscopy. Under a fluoroscope, the radiopaque coil will appear brightly.
The proximal end of the distal end coil is threaded into the distal end of the proximal coil. The coils are joined into a unitary assembly by brazing. The brazing also secures the coils to the core wire. The brazing however, fills the space between the coils and the wire over a length of the reduced diameter portion. This consequently increases the effective diameter of the core wire abruptly, thus changing the core wire's flexibility at the braze or solder.